Fixes: #119526.

This PR is to fix the SafeArea issue for the BottomAppBar. When MediaQuery.of(context).padding.bottom is not 0.0(such as on iOS platforms), the height of the BottomAppBar should add the bottom padding, so that the items on the bar can show correct shapes and positions. So to fix this, we should put the SizedBox inside of SafeArea, instead of the original way(The SizedBox is outside of the SafeArea).

The calculation of FloatingActionButtonLocation.endContained is also updated in this PR to respect the non-SafeArea(bottom padding).

After the fix:

Before the fix:

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.